This invention relates to arrangements for controlling the activation of deactivatable cams for the cylinder valves of an internal combustion engine.
German Offenlegungsschrift No. 39 20 938 discloses an arrangement for selectively controlling the operation of the cylinders of an internal combustion engine either by nonactuation of the valves for those cylinders or, in the case of cylinders having several inlet valves, closing selected intake passages by nonactuation of the corresponding valves, i.e., preventing the associated valves from opening at low engine speeds and in the partial-load range. A special advantage of the control arrangement disclosed in this reference is that it permits precise selection of the time of deactivation of the controlled valve. This is important because the deactivation of the selected valve cam must not interfere with the working cycle of the corresponding engine cylinder and, therefore, the deactivation must occur when the valve has at least approximately reached its closed position. The described arrangement obtains this result by a hydraulic circuit which is very simple since it utilizes the torque exerted on the cam by the valve-closing spring at a certain phase of the valve cycle, i.e., toward the end of its closing motion, to generate a force for disengagement of the teeth coupling the valve cam and the camshaft and thereby prepare for deactivation of the cam and its corresponding valve.
Since the valve cam is deactivated by the force exerted by the valve on the cam in accordance with its phase of operation, any difficulties which might occur regarding synchronization of the disengagement of the cam coupling with the working cycle of the valve are avoided.
It is apparent that the coupling between the cam and the camshaft must engage very rapidly to activate the cam and the corresponding valve, especially at high engine speeds.